First of all, we need to know what a chimney cricket is. Without spelling out the technical definition, let’s make it easy. It is a small peaked roof built on the backside, or high side, of a chimney to direct water and debris away. When a cricket is installed on your chimney, debris will be less likely to build up behind the chimney and therefore will not deteriorate your roof material.
A chimney cricket will help keep the back side of your chimney free of debris and water puddling or ponding. Picture this in early spring in a northern climate. Water trickling down the roof in the day time begins to freeze as the temperatures drop. Now if that water freezes right behind the chimney, you may have an ice dam issue. By having the chimney cricket, the water will be directed around the chimney, rather than gathered up directly behind it.
As a rule of thumb, chimney crickets are recommended on chimneys that are over 30′ wide. Do not be fooled by this rule however. If you are having problems with debris behind your chimney that is less than 30″ wide, you may still want to consider a chimney cricket. A good home inspector will note the absence or presence of a chimney cricket for you, and may also make recommendations as to the effectiveness of a chimney cricket.
If you are unable to access your roof to see behind your chimney, hire a home inspector or other chimney professional to do a proper examination of the area to see if a chimney cricket is needed behind your chimney. If a chimney cricket is needed, hire the proper professional to do the work for you, and have it inspected upon completion of the work or repair.